This invention is generally directed to the use of amorphous silicon compositions in electrophotographic imaging members, and more specifically, the present invention is directed to photoresponsive layered imaging members, or devices comprised of hydrogenated amorphous silicon and silicon oxides. In one embodiment of the present invention, there is provided a layered photoresponsive imaging member comprised of a supporting substrate, hydrogenated amorphous silicon, and in contact therewith a layer comprised of plasma silicon oxide. Further, in an alternative embodiment of the present invention, there is provided a layered photoresponsive imaging member wherein the plasma generated silicon oxide transporting layer is situated between a supporting substrate and the hydrogenated amorphous silicon layer. These imaging members can be incorporated into electrographic, and in particular xerographic printing systems, wherein the latent electrostatic images which are formed, can be developed into images of high quality, and excellent resolution. Moreover, these members possess high charge acceptance values, in excess of 1,000 volts, and the members can be of very desirable thickness from for example, of about 10 microns, or less. Also, the imaging members of the present invention have desirable low dark decay properties, and are thus very useful in xerographic imaging processes. In these processes, latent electrostatic images are formed on the devices involved, followed by developing the images with known developer cmpositions, subsequently transferring the image to a suitable substrate, and optionally permanently affixing the image thereto. The photoresponsive imaging members of the present invention, when incorporated into xerographic imaging, and printing systems, are insensitive to humidity conditions and corona ions generated from corona charging devices, enabling these members to generate acceptable images of high resolution for an extended number of imaging cycles exceedng, in most instances, more than 500,000 imaging cycles.
Electrostatographic imaging, and particularly xerographic imaging processes are well known, and are extensively described in the prior art. In these processes generally, a photoresponsive or photoconductor material is selected for forming the latent electrostatic image thereon. This photoreceptor is generally comprised of a conductive substrate containing on its surface a layer of photoconductive material, and in many instances, a thin barrier layer is situated between the substrate and the photoconductive layer to prevent charge injection from the substrate, which injection would adversely affect the quality of the resulting image. Examples of known useful photoconductive materials include amorphous selenium, alloys of selenium, such as selenium-tellurium, selenium-arsenic, and the like. Additionally, there can be selected as the photoresponsive imaging member various organic photoconductive materials, including for example, complexes of trinitrofluorenone and polyvinylcarbazole. Moreover, recently, there has been disclosed multilayered organic photoresponsive devices comprised of an aryl amine hole transporting molecule dispersed in an inactive resinous binder, and a photogenerating layer, reference U.S. Pat. No. 4,265,990, the disclosure of which is totally incorporated herein by reference. Examples of charge transport layers disclosed in this Patent include various diamines, while examples of photogenerating layers are trigonal selenium, metal and metal-free phthalocyanines, vanadyl phthalocyanines, squarine compositions, and other similar substances.
Additionally amorphous silicon photoconductors are known, thus for example there is disclosed in U.S. Pat. No. 4,265,991 an electrophotographic photosensitive member comprised of a substrate, a barrier layer, and a photoconductive overlayer of amorphous silicon containing 10 to 40 atomic percent of hydrogen and having a thickness of 5 to 80 microns. Further described in this patent are several processes for preparing amorphous silicon. In one process embodiment, there is prepared an electrophotographic sensitive member by heating the member in a chamber to a temperature of 50.degree. C. to 350.degree. C., introducing a hydrogen containing gas into the vacuum chamber, causing an electrical discharge by electric energy to ionize the gas, in the space of the chamber in which a silicon compound is present, followed by depositing amorphous silicon on an electrophotographic substrate at a rate of 0.5 to 100 Angstroms per second, thereby resulting in an amorphous silicon photoconductive layer of a predetermined thickness. While the amorphous silicon device described in this patent is photosensitive, after a minimum number of imaging cycles, less than about 10, for example, unacceptable low qaulity images of poor resolution, with many deletions, result. With further cycling, that is, subsequent to 10 imaging cycles and after 100 imaging cycles, the image quality continues to deteriorate, often unit images are partially deleted. Accordingly, while the amorphous silicon photoresponsive device of U.S. Pat. No. 4,265,991 patent is useful, its selection as a commercial device which can be used functionally for a number of imaging cycles is not readily achievable.
There is also disclosed in a copending application, U.S. Ser. No. 524,801, the disclosure of which is totally incorporated herein by reference, imaging members comprised of compensated amorphous silicon compositions, wherein there is simultaneously present in the amorphous silicon dopant materials of boron and phosphorous. More specifically there is disclosed in the copending application a photosensitive device comprised of a supporting substrate, and an amorphous silicon composition containing from about 25 parts per million by weight to about 1 weight percent of boron, compensated with from about 25 parts per million by weight to about 1 weight percent of phosphorous.
Moreover, disclosed in U.S. Pat. Ser. No. 4,544,617, the disclosure of which is totally incorporated herein by reference, is an imaging member comprised of a supporting substrate, a carrier transport layer comprised of uncompensated or undoped amorphous silicon, or amorphous silicon slightly doped with p or n type dopants such as boron or phosphorous, a thin trapping layer comprised of amorphous silicon which is heavily doped with p or n type dopants such as boron or phosphorous, and a top overcoating layer of silicon nitride, silicon carbide, or amorphorous carbon, and wherein the top overcoating layer can be optionally rendered partially conductive.
While the above described imaging members, particularly those disclosed in the copending applications are suitable for their intended purposes, there continues to be a need for improved imaging members comprised of amorphous silicon. Additionally, there is a need for very thin imaging members of amorphous silicon compositions less than, for example about 10 mircons in thickness, that posses desirable high charge acceptance and low charge acceptance loss in the dark. Also there is a need for layered imaging members comprised of amorphous silicon photogenerating substances, and in contact therewith charge transport layers. Furthermore there continues to be a need for improved amorphous silicon imaging members with silicon oxide, and wherein there is introduced into the silicon oxide charge transport layer electronic defect states by stoichiometric control of dopants, (impurities) of sufficient density enabling transport to be accomplished by hopping between the resulting localized states. These states are positioned within the band gap of the silicon oxide itself, thus the injection of carriers from the amorphous silicon photogenerating layer can be more easily effected by, for example, choice of the defect state, and by compositional grading of the interface between the photogenerating and transport layer. Additionally there continues to be a need for improved layered imaging members of amorphous silicon which are humidity insensitive and are not adversely effected by electrical consequences resulting from scratching and abrasion. There is also a need for amorphous silicon imaging members which can be selected for use in repetitive imaging and printing systems. Furthermore there is a need for amorphous silicon imaging members with the property of low surface potential decay rates in the dark, and yet are photosensitive in the visible and near visible wavelength range.